This invention relates to (a) the fine powder of high molecular weight fluorine containing fused resins (this fine powder is especially suitable in producing jigs, etc. used in the manufacturing processes of semiconductors), (b) mold goods obtained by molding this fine powder, and (c) these production methods.
Inasmuch as fluorine containing fused resins are especially excellent in heat resistance, chemical resistance, electrical insulation, nonviscous property, lower friction property, etc. among many kinds of plastics, they are applied in fields ranging from the space development and aircraft industries to the household goods industry, chemical industry, the electric and electronic industries, and the machine industry.
It is comparatively difficult, however, to mold fluorine containing fused resins because they have higher melt viscosities and narrower ranges of proper mold processing conditions as compared with other general-purpose plastics. Such resins, moreover, may decompose slightly at high molding temperatures to produce corrosive gases. Especially, as high molecular weight resins having a melt viscosity of 106 or greater poise are excessively high in melt viscosity and very low in fluidity, it is very difficult to mold them by ordinary extrusion molding and injection molding. As a result, these resins have so far been without an application.
Conversely, as appreciated from the case of superhigh molecular weight polyethylene, plastics generally develop merits with increased molecular weight. It is thus possible to improve mechanical properties, including strength, modulus of elasticity, abrasion resistance and resistance to flex fatigue; and to improve chemical properties such as weatherability and chemical resistance. It is therefore naturally expected that valuable improvements of properties can be achieved also in fluorine containing fused resins by increasing their molecular weight. Such improvements, however, have not been utilized practically because of the above-mentioned molding difficulty. Rather, techniques of lowering the molecular weight of fluorine containing resins have been studied while maintaining their mechanical and chemical properties.
Furthermore, although fluorine containing fused resins are usually molded by extrusion and injection, the resins are supplied in the form of pellets, as with other general-purpose plastics. This is done to secure a good supply of raw materials for molding machines, including facile dropping through hoppers and feeding into the screws, and to make the handling of raw materials easy.
High molecular weight resins, however, having melt viscosities of 106 or greater poise are difficult to pelletize because of excessive melt viscosity.
Accordingly, there exists no alternative to their being supplied in the form of powder as they are. Powder, however, immediately following polymerization has low apparent density and inferior fluidity, making its supply unstable. This has also been a factor obstructing the practical use of high molecular weight fluorine containing fused resins.
Conversely, inasmuch as fluorine containing fused resins have the above-mentioned excellent properties, it is the ingredient of choice in the manufacturing processes of semiconductors as mold goods such as wafer carriers, tubes, joints, square brackets, etc. Because LSI is highly integrated and concentrated, minute amounts of impurities such as particles, metals, etc. have come into question. Concerning mold goods of fluorine containing fused resins used in these applications, the demand for high purity is also increasing.
Accordingly, the liquation of particles from mold goods of fluorine containing fused resins is a problem. Proposed to decrease the number of liquated particles have been a method for extracting these particles with a fluorine-containing solvent, and a method of washing mold goods with isopropyl alcohol, etc. Both methods, however, have problems in cost and productivity because they are after-treatments conducted by means of special equipment and chemical liquids.
The purposes of this invention are (a) to improve the properties of fine powder of high molecular weight fluorine containing fused resins that have not been utilized, (b) to offer mold goods that have diminished numbers of liquated particles and that are preferable to the manufacturing processes of semiconductors by molding the fine powder, and (c) to offer the production methods of these mold goods.
This invention thus relates (a) to the fine powder of high molecular weight fluorine containing fused resins having melt viscosities of 106 to 1010 poise, apparent densities of 0.4 to 1.5 g/cc, and specific surface areas of 2 m2/g or less; and (b) to mold goods obtained by molding the fine powder.
As the kinds of fluorine containing fused resins in this invention, at least one kind of resins are given that are selected from the resin group composed of copolymers of tetrafluoro ethylene and perfluoro alkylvinyl ether (hereinafter xe2x80x9cPFAxe2x80x9d), copolymers of tetrafluoroethylene and hexafluoropropene (hereinafter xe2x80x9cFEPxe2x80x9d), copolymers of tetrafluoro ethylene and ethylene (hereinafter xe2x80x9cETFExe2x80x9d), vinylidene fluoride homopolymers (hereinafter xe2x80x9cPVDFxe2x80x9d), copolymers of vinylidene fluoride and tetrafluoro ethylene, copolymers of vinylidene fluoride and hexafluoropropene, copolymers of vinylidene fluoride and chlorotrifluoroethylene, copolymers of chlorotrifluoroethylene and ethylene (hereinafter xe2x80x9cECTFExe2x80x9d), etc. Here, a copolymer PFA is preferable to be a copolymer of tetrafluoro ethylene and at least one kind of perfluoro alkylvinyl ethers as expressed by the formula CF2xe2x95x90CFO(CF2)mF (in this formula, m is an integral number of one to six), or a formula CF2xe2x95x90CF(Oxe2x80x94CF2CF(CF3))nOC3F7 (in this formula, n is an integral number of 1 to 4); and is especially preferable to be a copolymer of tetrafluoro ethylene of 92% to 99% and perfluoro alkylvinyl ether of 1% to 8% by weight. Further, FEP is preferable to be a copolymer of tetrafluoro ethylene of 72% to 96% and hexafluoropropene of 4% to 28% by weight. ETFE is preferable to be a copolymer of tetrafluoro ethylene of 74.5% to 89.3% and ethylene of 10.7% to 25.5% by weight. These fluororesins are allowed to be copolymerized with other monomers in an amount not adversely to affect the essential properties of each resin. As the other monomers, the following compounds are given as examples: (a) tetrafluoro ethylene, (b) chlorotrifluoroethylene, (c) hexafluoropropene, (c) perfluoro alkylvinyl ether, (d) fluoroalkyl (C1 to C10) ethylene, (e) perfluoroalkyl (C1 to C10) allyl ether, (f) compounds expressed by the formula CF2xe2x95x90CF[OCF2CFRf(CF2)p]qOCF2(CF2)rY (in this formula, Rf is fluorine atom or trifluoro methyl radical, Y is a halogen atom, p is 0 or 1, q is 0 or an integral number of 1 to 5, r is 0 or an integral number of 1 to 2. When, however, p is 1, Rf is fluorine atom), and (g) compounds expressed by the formula CH2=CF(CF2)nX (in this formula, n is an integral number of 0 to 8, and X is a hydrogen or fluorine atom).
The melt viscosity of fluorine containing fused resins in this invention must indispensably be 106 to 1010 poise from the point of view of decreasing the number of liquated particles and improving the quality of mold goods,. Those resins having melt viscosity of less than 106 poise, which are collectively called fluorine containing fused resins and are usually commercially available for mold processing, are not preferable because they have lower mechanical properties and large numbers of liquated particles as will be mentioned later. Furthermore, in case of resins having melt viscosities of more than 1010 poise, their mold processing temperatures cannot help being increased over the starting temperatures of their thermal decompositions to obtain favorable mold goods. Accordingly, these resins are not preferable because their mold goods are foamed and colored.
Generally, resins of high molecular weights that have not hitherto been usedxe2x80x94those having melt viscosities of more than 106 poisexe2x80x94are objects of this invention. The polymerization methods, however, of fluorine containing fused resins to be used in this invention are unlimited. Generally well-known methods, such as emulsion polymerization, suspension polymerization, solution polymerization, and bulk polymerization, can be used in producing the resins.
The apparent density of the fine powder of fluorine containing fused resins in this invention must indispensably be 0.4 to 1.5 g/cc from the point of view of powder fluidity, moldability,and improving the quality of mold goods, and is preferably 0.5 to 1.4 g/cc. Those resins having apparent density of less than 0.4 g/cc show bad powder fluidity and are apt unevenly to be filled in dies in case of injection molding and compression molding, resulting in failure to produce favorable mold goods. Further, those resins having apparent densities exceeding 1.5 g/cc also do not produce favorable mold goods because the powder particles cannot sufficiently be mutually welded.
The specific surface area of the fine powder of fluorine containing fused resins in this invention must indispensably be 2 m2/g or less from the point of view of powder fluidity, and preferably should be 1 m2/g or less. If the specific surface area is greater than 2 m2/g, powder fluidity is low as a result of insufficient firmness of the powder particles. Such powder is not preferable especially for molding with screws, such as in injection molding, because the powder is insufficiently taken into the screws. The average particle size ranges from 10 to 2,000 xcexcm and preferably would be from 50 to 1,000 xcexcm
The raw material powder of fluorine containing fused resins (raw powder) just after polymerization (after coagulation in case of emulsion polymerization) has insufficient firmness with an apparent density of less than 0.4 g/cc and a specific surface area exceeding 2 m2/g. Accordingly, for the above-mentioned reason, this raw powder cannot be supplied to molding machines because it requires increased apparent density and decreased specific surface area.
As methods in this treatment, the following examples are shown. Raw powder of high molecular weight fluorine containing fused resins is heated at temperatures between (m.p.xe2x88x9210xc2x0 C. ) and (m.p.+20xc2x0 C.), preferably at temperatures between m.p.+10xc2x0 C. , to be welded partially. Then the raw powder is ground. On this occasion if raw powder is heated at temperatures exceeding m.p.20xc2x0 C., it will be welded excessively and become difficult to grind, resulting in decreased apparent density. Further, if raw powder is heated at temperatures below(m.p.xe2x88x9210xc2x0 C.), it will be welded insufficiently, resulting in failed diminished specific surface area as a result of inadequate firmness.
Furthermore, it is possible to adopt a method whereby raw powder of high molecular weight fluorine containing fused resins is rolled at temperatures below (m.p.xe2x88x9210xc2x0 C.), and under pressures of preferably 2 kg/cm2 or more, to make compressed plate-like products, which are finally ground. Although no restriction will be imposed on the method of grinding, and ordinary grinders can be used, it is preferable to use a Henschel grinder, rotor speed mill, etc.
According to these methods, it is possible to obtain a fine powder of high molecular weight fluorine containing fused resins with apparent densities of 0.4 to 1.5 g/cc and specific surface areas of 2 m2/g or less. This fine powder has good powder fluidity and will ensure a good supply of raw materials to molding machines. Accordingly, the following kinds of molding will become possible.
Only a small change is needed for conventional molding methods to use them as molding methods in this invention, despite the fact that the fluorine containing fused resins to be used have the above-mentioned properties.
The applicable molding methods include compression molding, isostatic molding, transfer molding, ram extrusion molding, extrusion molding, injection molding, blow molding, and flashflow molding.
Molding conditions vary depending on each molding method. Inasmuch, however, as resins of this invention are high in molecular weight and melt viscosity, it is preferable to raise the molding temperatures and die temperatures by 10xc2x0 to 60xc2x0 C. , and to raise the molding pressures by 50 to 100 kg/cm2 while injection time and pouring time are decelerated by 10 to 100 sec. and the cooling time lengthened by 50 to 100 sec., compared with the molding conditions for conventional fluorine containing fused resins. Molding temperatures must be kept below the thermal decomposition starting temperatures of the resins to be used to prevent mold goods from being foamed and colored.
According to these molding methods, mold goods having desired shapes can be obtained. These include mold goods of complicated shapes such as wafer carriers, wafer boxes, bolts, beakers, filter housings, flowmeters, pumps, valves, cocks, connecting joints, connectors, and nuts; as well as simple mold goods such as sheets, films, gasket, rods,square rods, pipes, tubes, electric wires, circular brackets, square brackets, and tanks.
The mold goods based on this invention are those obtained by using high molecular weight resins that have thus far not been utilized. Accordingly, the rate of lower molecular weight materials in resins has diminished relatively.
Meanwhile, as the main cause of the occurrence of liquated particles from mold goods, which has come into question in the manufacturing processes of semiconductors, it is pointed out that lower molecular weight materials in the resins dissolve in chemical liquids. Accordingly, mold goods based on this invention are best suited for the manufacturing processes of semiconductors because they have a small number of liquated particles.
The fine powder of high molecular weight fluorine containing resins based on this invention is the fine powder of high molecular weight fluorine containing fused resins having a melt viscosity of 106 to 1013 poise, apparent density of 0.4 to 1.5 g/cc, and specific surface area of 2 m2/g or less, such as not previously been used. Accordingly, mold goods obtained by employing this fine powder have fewer liquated particles and are particularly suited for the manufacturing processes of semiconductors. Furthermore, it will be also possible to improve the properties of the mold goods, such as flex fatigue resistance and abrasion resistance.